Maverick Nationals senator warns Malcolm Turnbull to 'sit up and take note' on banking commission

Coalition Senator defying the PM Nationals senator Barry O'Sullivan plans to put forward legislation for an inquiry into the banks, going against government policy and says he has the support of colleagues.

Nationals senator Barry O'Sullivan says he is committed to bringing on a powerful commission of inquiry into the banking sector, predicting up to four MPs in the House of Representatives could cross the floor and support his bill.

Warning Prime Minister Malcolm Turnbull to "sit up and take note" if the Parliament backs the measure in defiance of the government, Senator O'Sullivan said the government's adoption of a conscience vote on same-sex marriage had opened up a new tactic for Coalition MPs who support taking on the nation's banks.

"The introduction of [Senator Dean Smith's bill to legalise same-sex marriage] into the Senate showed a new pathway for backbenchers to be able to pursue matters of importance to them and I'm just simply following along in his footsteps," Senator O'Sullivan told ABC radio on Monday morning.

"If both houses of the Parliament think this is a good thing to do and that is the decision, I think the Prime Minister has to sort of sit up and take note and support the parliamentary decision," he said.

Senator Barry O'Sullivan Photo: Alex Ellinghausen: ABC RN

Senator O'Sullivan said it had been an "untidy year" in federal politics but declined to say whether his bill passing the Parliament would undermine the Turnbull government, which has resisted such an examination of the sector.

"I'm more concerned about the Parliament functioning. We're talking about the Parliament here, not the government. The people of Australia are sick to their [back] teeth of the Parliament not functioning.

Now, if a bill passes both the Senate and the House of Representatives, that suggests that the Parliament is functioning," he said.

"So I'm not going to be drawn on the question of the impacts on the Prime Minister and our government. This is about democracy at work."

Labor and the Greens are likely to back the move for a commission of inquiry, which is comparable to a royal commission but reports to the Parliament rather than the government.

But Opposition Leader Bill Shorten maintained a royal commission would be the "king of all inquiries".

"I have got no doubt that there are Coalition members itching to vote for a banking royal commission," he said on Monday.

"Because of the citizenship chaos in the government, because of the constitutional crisis that Mr Turnbull and his government have inflicted upon the Parliament, there is a window of opportunity for Labor and like-minded people who want a banking royal commission to finally do what Australians want."

Senator O'Sullivan said there "could be as many as four" Coalition MPs in the lower house who would back his new bill, including Queenslanders George Christensen and Llew O'Brien. Nationals-aligned MPs Ken O'Dowd and Luke Hartsuyker and Liberal-aligned Warren Entsch have also indicated support for a banking royal commission in the past.

An absolute majority of 76 MPs would be required to suspend standing orders to bring on debate in the House of Representatives about Senator O'Sullivan's private members bill. Labor and the crossbench could provide 74 votes, meaning only two votes are needed from the Coalition side.

The inquiry would scrutinise Australia's banking and financial sector and examine the litany of scandals that have plagued Australia's big banks, including the revelations concerning Commonwealth Bank financial planning and CommInsure life insurance.